Disk drives are widely used in computers and data processing systems for storing information in digital form. These disk drives commonly use one or more rotating storage disks to store data in digital form. Each storage disk typically includes a data storage surface on each side of the storage disk. These storage surfaces are divided into a plurality of narrow, annular regions of different radii, commonly referred to as “tracks”. The disk drive includes a head stack assembly having a positioner, an actuator assembly and one or more transducer assemblies. The actuator assembly includes an actuator hub, an actuator pivot center, and one or more actuator arms. Each transducer assembly includes one or more data transducers. The positioner is used to precisely rotate the actuator assembly to position the data transducers relative to one or more storage disks. The data transducer transfers information to and from the storage disk when precisely positioned over an appropriate data track (also referred to as a “target track”) of the storage surface.
The need for increased storage capacity and compact construction of the disk drive has led to the use of disks having increased track density, i.e. more tracks per inch. As the track density increases, the ability to maintain the data transducer over the target track becomes more difficult. More specifically, as track density increases, it is necessary to reduce positioning error of the data transducer proportionally. With these systems, the accurate and stable positioning of the data transducer proximate the appropriate track is critical to the accurate transfer and or retrieval of information from the rotating storage disks.
Conventional positioners include a voice coil motor. The voice coil motor works by directing electrical current through a wound wire coil located in a magnetic field. Besides causing the actuator arms and transducer assemblies to move in a desired direction, the same coil forces excite one or more undesirable vibration modes, including for example, a “first vibration mode ” and a “second vibration mode”. In some drives, the first vibration mode occurs at a frequency of between approximately 5,000 and 7,500 cycles per second and the second vibration mode occurs at a frequency of between approximately 7,500 and 12,000 cycles per second. These vibration modes can cause an undesirable vibration displacement of the data transducer, and can therefore make it more difficult to accurately maintain positioning of the data transducer over the desired track of the storage disk (also known as “track following”). Much of this vibration is caused by the structural response of the actuator assembly to forces in the coil that are used to position the data transducers.
One attempt to increase the level of accuracy in positioning the actuator assembly and the transducer assembly relative to the storage disk includes using a so-called “pure torque ” positioner, i.e. generating theoretical forces with one or more coils that are equal but directionally opposite relative to the actuator hub. In theory, the directionally opposite forces reduce excitation of the first vibration mode at the actuator hub. However, this theory assumes that the positioner and the actuator assembly are a purely rigid, completely inflexible body, and the first vibration mode motion is a rigid body translation motion. Unfortunately, because the positioner and the actuator assembly are not completely rigid, the first vibration mode is not satisfactorily inhibited.
Another attempt to increase accuracy of the positioner includes using two coils through which current is directed in opposite directions. The currents are adjusted to generate forces that nearly cancel one another. In order to maintain the data transducer on a particular track, an increased current is directed through one of the coils to move the data transducer toward the center of the data track. However, because this design utilizes two or more relatively large, geometrically similar coils, increased power is required during track following because both coils are used in an offsetting manner. This increased power consumption can increase the cost of using the disk drive and the heat generated within the disk drive.
In light of the above, the need exists to provide a positioner that accurately positions and maintains the data transducer relative to the target track of a storage disk while using relatively low power consumption. A still further need exists to reduce the cost of manufacturing a high-density disk drive.